Machines used primarily in industrial applications, such as hydraulic excavators, bulldozers, backhoes, loaders, graders compactors and the like, have been designed with increasingly more complex control systems. The additional complexity allows the machines to perform assigned tasks more efficiently and precisely. For example, excavators can move more material within a given time period while moving material only within a defined boundary area. However, using traditional operator controls, such as joysticks and foot pedals, the efficiency and precision of machines are limited by both the controls themselves and operator proficiency.
Computing devices have been used to further improve the operation and efficiency of such machines. These computing devices may be configured to monitor and control various operating characteristics of the machines. For example, engine operation, torque transfer and work tool movement may all be electronically controlled. One of the constraints on use of computing equipment, however, is that it is required to withstand extreme operating conditions. For example, such machines are sometimes exposed to great temperature variation. Further, machines are often deployed in wet, dirty, and other adverse environments.
Often, such machines require relatively high voltage electrical power distribution among the batteries and various loads of the machine. These circuits can potentially short circuit various machine components, including circuits used in low power applications such as the computing equipment. Under these conditions, computing devices can be destroyed by prolonged short circuit conditions applied by virtue of malfunction of the machine's high voltage electrical power systems.
Various circuits have been designed to protect computing devices in traditional environments where such equipment is used, such as in office environments and the like. These circuits are typically designed for protection from transient over-voltage conditions. For example, such circuits may provide protection from electro static discharge. However, they are not designed to protect sensitive computing devices from steady state or long term over-voltage conditions, such as the application of a continuous short circuit to the main electrical power system of a machine.
Other over-voltage protection circuits have been used to protect computing equipment from continuous short circuits to high voltage power sources. For example, U.S. Pat. No. 6,788,506 to Stockstad discloses an over-voltage protection circuit that is implemented on the same integrated circuit as the computing equipment it is intended to protect. The circuit is part of an integrated circuit implementing a USB controller for an associated computer. Stockstad, however, does not allow the protection circuit to be retrofitted for use with any computing equipment and any input to the computing equipment. Further, Stockstad reduces the voltage of an over-voltage signal and transmits the reduced voltage version of the signal. For certain conditions such as a prolonged over-voltage condition, therefore, Stockstad does not adequately protect the computing equipment. Stockstad is susceptible to passing an incorrect logic value to the computing equipment. For example, if the signal had been 0.3 volts, representing a logical 0 to the computing equipment, a short circuit condition may have raised the signal to a much higher value, such as 10 volts. Stockstad then reduces this value to 3.3 volts, representing a logical 1 to the computing equipment. Therefore, the computing equipment would process incorrect data, which may cause a failure of the machine.